Class12

# Class12 - Review You are at a party being held outside an...

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2/3/12 Oregon State University PH 202, Lecture 12 1 Review : You are at a party being held outside an apartment building. Two outdoor loudspeakers are emitting a single tone (in phase) of 171.5 Hz. Speaker A is at ear level. Speaker B is sitting on a balcony, exactly 4 m above speaker A. Standing 3 m from speaker A, what would you hear? [Assume the speed of sound is 343 m/s.] 1. (completely) Constructive Interference 2. (completely) Destructive Interference 3. interference that is neither completely constructive nor completely destructive. 4. Giants win by a field goal in OT .

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2/3/12 Oregon State University PH 202, Lecture 12 2 Other Effects of Interference We have seen the one-time effects of interference: reinforcement or reduction in amplitude of superimposed waves via phase shifts and path differences. But interference also has other interesting and useful consequences: beats , diffraction and standing waves . Beats The phenomenon of beats is a very simple one but is very helpful for tuning and measuring slight frequency differences. A beat is an alternating rise and fall in the observed amplitude of the combined (superimposed) sound of two sources that are close, but not identical, in frequency. The lows and highs of the two functions occur together only rarely—just a few cycles per second—so that we can hear distinctly each combined high (constructive interference) or low (destructive interference).
2/3/12 Oregon State University PH 202, Lecture 12 3 It turns out that the frequency of the beats is simply the difference in the frequency of the two sources:

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Class12 - Review You are at a party being held outside an...

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